TUESDAY, April 27 (HealthDay News) -- Adults who undergo a sigmoidoscopy examination between ages 55 and 64 could significantly reduce their odds of developing and dying from colorectal cancer, new research shows.

Flexible sigmoidoscopy enables doctors to look for cancers and symptomless growths called adenomas in the rectum and sigmoid (lower) colon, where two-thirds of colorectal cancers occur. Sigmoidoscopy does not examine the upper colon, as colonoscopy does.

Noting that most people with distal colon cancer (rectum and lower colon) will have developed an adenoma by age 60, the researchers theorized that removing adenomas through sigmoidoscopy would provide lasting protection.

In a long-term study, British researchers found that having the cancer-screening test just once in that age range reduced the incidence of colorectal cancer by one-third.

"The results from our trial show that flexible sigmoidoscopy is a safe and practical test and, when offered only once to people between ages 55 and 64 years, confers a substantial and long-lasting protection from colorectal cancer," the authors wrote in a study released online April 27 in advance of publication in an upcoming print issue of The Lancet.

Colorectal cancer is the third most common cancer worldwide (fourth in the United States), resulting in one million diagnoses and 600,000 deaths a year. Survival rates are good for cancers that haven't spread, so early detection is key.

Many countries promote fecal occult blood tests for early screening, but that technique reduces mortality by only 15%, according to background information in the study.

For their study, begun nearly 16 years ago and conducted in England, Wales and Scotland, the research team followed almost 113,000 men and women in a control group and another 57,099 participants in an intervention group, of which 40,674 (71%) underwent flexible sigmoidoscopy.

Over an average 11 years of follow-up, 2,524 participants were diagnosed with colorectal cancer (1,818 in the control group and 706 in the intervention group). Deaths certified from colorectal cancer totaled 727 (538 in the control group, and 189 in the intervention group), the study authors noted.

Incidence of distal colorectal cancer fell by 50%. Cases of colorectal cancer among those screened were reduced by 33% and deaths by 43%, the authors said.

"Confining results to the rectum and sigmoid (lower) colon, incidence was reduced by half in those who were screened," wrote Wendy Atkin of Imperial College London, and colleagues.